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import data into GAMMA
Added by Cynthia Chen almost 4 years ago
Dear GAMMA users,
I want to process the files like coherence map, phase map, ls_map and so on in MATLAB to do some calculation. Then I want to put the processed data into GAMMA, so that I can use look-up table to transform them from SAR coordinate to map coordinate (and vice versa).
I can use swap_byte to export the data to MATLAB. But I don't know how to import the processed data into GAMMA.
Very appreciate if you can help me. Thank you so much.
Replies (3)
import data into GAMMA - Added by Charles Werner almost 4 years ago
Hello,
The input data to Gamma is Big Endian Float (4/bytes per value). In Matlab you
can export data as Big Endian, or you can swap the bytes with the Gamma program
called (not surprisingly) swap_bytes to come back. swap_bytes does not care if
the data are big- or little-endian as input.
Note that the geocoding lookup table created by the rdc_trans consists of pairs
of 4-byte float numbers that gives you the range and azimuth coordinates for
every point in the map projection or geographic coordinate system.
- DISP swap_bytes: swap bytes for binary format data ***
- Copyright 2005, Gamma Remote Sensing, v1.8 13-Oct-2005 uw/clw ***
usage: swap_bytes <infile> <outfile> <swap_type>
input parameters:
infile (input) input data file
outfile (output) output data file
swap_type swap type flag (bytes/value)
2: (1,2,3,4,5,6,7,8...) --> (2,1,4,3,6,5,8,7...) (SHORT, SCOMPLEX)
4: (1,2,3,4,5,6,7,8...) --> (4,3,2,1,8,7,6,5...) (INT, FLOAT,
FCOMPLEX)
8: (1,2,3,4,5,6,7,8...) --> (8,7,6,5,4,3,2,1...) (DOUBLE)
RE: import data into GAMMA - Added by Cynthia Chen almost 4 years ago
Dear Charles,
Thank you so much. Now I can import the processed data into GAMMA following your way.
I have another question that I want to use Sentinel and ALOS-2 data to generate DEMs separately. Can I also refer to the process of TanDEM-X data?
1. Create a differential interferogram of the scene with the existing DEM and
unwrap the phase.
2. use the program dh_map_orb to calculate the correction based on the unwrapped
differential phase
3. update the DEM in the regions where there is unwrapped phase.
RE: import data into GAMMA - Added by Charles Werner almost 4 years ago
Hello,
Yes, I think you can... It is a general approach to improving an existing DEM,
or maybe finding changes in DEM due to a landslide or receding glacier.
It is always easier to unwrap a differential interferogram.
One point that I did not mention is that you should select one region in the
differential interferogram as the reference area, where the height difference is
set to 0.0. There is always an unknown phase constant in interferograms related
to errors in state vectors and phase delay through the atmosphere as well as
changes in the radar electronics. For that reason there is an unknown phase
constant that must be set. After you have measured the phase of the patch in the
differential interferogram, subtract that average phase value from the entire
interferogram.
If there is a tilt in the phase due to inaccurate baseline, you can try to
estimate a residual baseline from the unwrapped phase and known heights of
different areas, or use quad_fit to remove a polynomial residual phase model.
Best regards,
Charles